Measuring probe and method for filling a probe interior

ABSTRACT

The present disclosure relates to a measuring probe for measuring a concentration of an analyte in a measuring medium represented by a measured variable, including a probe housing having a first housing part and a second housing part, the first housing part being cap shaped closed on a front end by a sensor membrane and detachably connected to the second housing part on a rear end opposite the front end, such that the second housing part closes the cap at the rear end, and the first and the second housing parts define a probe interior sealed by the sensor membrane, a fluid electroyte contained within the probe interior, an overflow channel in communication with the probe interior, and a seal adjacent the probe interior so as to seal the probe interior from the exterior of the measurement probe and simultaneously seal off the overflow channel.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is related to and claims the priority benefit ofGerman Patent Application No. 10 2016 120 581.8, filed on Oct. 27, 2016,the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a measuring probe and a method forfilling the probe interior of a measuring probe in a substantiallygas-bubble-free manner.

BACKGROUND

Amperometric sensors can be used to determine a measured variabledependent upon the concentration of an analyte, such as theconcentration or activity of the analyte or of a parameter, inparticular, of a sum parameter that involves the concentration oractivity of the analyte. The measuring medium can be a measuring fluid,e.g., a measuring liquid or a measuring gas. Typical analytes, whoseconcentration or activity or measured variables dependent upon them canbe monitored using amperometric sensors, are, for example, gases such asoxygen, chlorine, carbon dioxide, hydrogen sulfide, ammonium, ornitrogen oxide.

Such sensors often have an amperometric measuring probe that is broughtinto contact with the measuring medium for example, by immersion in themeasuring medium. The measuring probe can include a measuring circuit,in particular, an on-site electronics unit that forms one of themeasured variable-dependent measurement signals and is equipped to emitthe measurement signal, or a signal derived from it using an initialprocessing, via an interface to a higher-level data processing device.The measuring probe having the measuring circuit can be connectedwirelessly or via a line to a remote measuring transducer, which furtherprocesses the measurement signal of the measuring probe and outputs itvia a user interface or a higher-level unit connected to the measuringtransducer for wireless or hardwired communication, e.g., a processcontroller or a programmable logic controller.

Amperometric measuring probes usually have a probe interior spaceseparated from the measuring medium by a sensor membrane also designatedherein as an electrolyte chamber as well as at least two, often alsothree, electrodes arranged within the probe interior space. Theelectrodes are connected in an electrically conductive manner to themeasuring circuit.

One of the electrodes functions as the measuring or working electrode,an additional one as a counter electrode. The sensor membrane generallyincludes at least one functional layer functioning as a diffusionbarrier through which the analyte is diffused from the measuring mediuminto the electrolyte chamber. The measuring circuit creates themeasurement signal that represents the measured variable, e.g., theanalyte concentration, on the basis of a current flowing through theelectrolyte between the measuring electrode and the counter electrode.In many amperometric applications, the potential of the measuringelectrode or the current flow between the measuring electrode and thecounter electrode through the electrolyte is regulated using a thirdreference electrode, through which current does not flow.

An amperometric measuring probe is described in, for example, DE 10 2008039465 A1. Accommodated inside the electrolyte chamber of the measuringprobe that is sealed by the sensor membrane is a fluid electrolyte withwhich the two or three electrodes are in contact. One of theseelectrodes acts as a measuring electrode. It is integrated into arod-shaped electrode body, which isolates the measuring electrode inrelation to the electrolyte, with the exception of its end face. Theelectrode body extends into the electrolyte chamber, wherein the endface of the measuring electrode abuts the sensor membrane. In thismanner, a thin electrolyte film forms between the sensor membrane andthe, for this purpose, optionally roughened or textured end face of themeasuring electrode. The intermediate, electrolyte-filled space thusformed between the end face of the measuring electrode and the membraneis here and in the following described as a measuring chamber.

The measuring probe has a first housing part designed in the form of acap and a second housing part that forms a probe. The first housing partincludes the sensor membrane and is designated as the membrane module ormembrane cap. The first and the second housing parts are detachablyconnected to one another via a screw connection. The detachableconnection allows for replacement of the first housing part by anidentically designed housing part, and thus for a replacement of themembrane.

If there are gas bubbles in the fluid electrolyte that is containedwithin the probe interior, there is a risk that they could pass into themeasuring chamber formed between the end face of the electrode body andthe sensor membrane. In the operation of the measuring probe, this leadsto an interference in the current flowing between the measuringelectrodes, and thus in the measurement signal of the measuring probe.This can adversely affect measurement precision, or even makemeasurement using the measuring probe impossible.

Care must therefore be taken to insure that the inclusion of gas bubblesin the probe interior is avoided during manufacture of the measuringprobe, or possibly during an exchange of the housing part containing thesensor membrane that takes place during maintenance. Amperometricmeasuring probes known in the prior art have, for this purpose, apressure relief valve that closes the probe interior. The membrane capis filled with electrolyte before connection to the probe shaft, whereinthe electrolyte volume filled into the membrane cap is greater than thevolume of the probe interior formed after the connection of the membranecap to the probe shaft. During connection of the membrane cap to thesecond housing part that forms the probe shaft, the second housing partseals the membrane cap while forming the probe interior, electrolyteexiting from the electrolyte chamber via the pressure release valve. Inthis manner, it is ensured that the probe interior is fully filled withfluid electrolyte, so that no gas bubbles remain in the probe interior.In the event of a malfunction of the pressure relief valve because ofdamage to or deterioration of the valve, for example, it cannot beensured that the probe interior is reliably sealed with respect to themeasuring medium, and that an intrusion of measuring medium into theprobe interior or an exit of electrolyte from the probe interior intothe measuring medium is reliably prevented.

SUMMARY

It is therefore the aim of the present disclosure to specify a genericmeasuring probe and a method for filling the probe interior withelectrolyte that avoid these disadvantages.

This aim is achieved by a measuring probe according to claim 1 and themethod according to claim 14. Advantageous embodiments are listed in thedependent claims.

The measuring probe for measuring a concentration of an analyte in ameasured variable representing a measuring medium comprises: a probehousing, which has at least a first housing part and a second housingpart, wherein the first housing part is designed in the shape of a cap,in particular, a cylindrical one which is closed on a front end by asensor membrane and, on a rear end opposite the front end, is detachablyconnected, specifically by a screw or plug connection to the secondhousing part so that the second housing part closes the cap at its rearend, and the first and the second housing parts enclose the probeinterior sealed by the sensor membrane; a flowable electroyte, inparticular, a fluid one contained within the probe interior; at leastone overflow channel that leads into the probe interior; and a sealwhich, at a wall of the first housing part and at a wall of the secondhousing part, seals the probe interior off from the area surrounding themeasurement probe and simultaneously seals off the overflow channel.

If an overflow channel opening into the probe interior is provided, uponassembly of the first and the second housing parts during themanufacture of the measuring probe, or when the first housing part isreplaced for the purpose of upgrading the sensor membrane, thecap-shaped first housing part can be filled with a volume of fluidelectrolyte that is larger than the volume of the probe interior that isenclosed by the interconnected first and second housing parts. In theconnection of the two housing parts, the excess volume of electrolyte isexpelled from the probe interior via the overflow channel. In thismanner, the inclusion of gas bubbles in the electrolyte-filled probeinterior can be avoided. In contrast to measuring probes known in theprior art, a pressure relief valve between the probe interior and themeasuring medium can be omitted if the overflow channel is closed by aseal that simultaneously acts to seal the probe interior enclosed by theinterconnected first and second housing parts. In this manner, theinclusion of gas bubbles in the probe interior during manufacture ormaintenance of the measuring probe can be avoided on the one hand, andon the other, it can be ensured that the probe interior is sealed withrespect to the measuring medium by the seal during operation, so thatthe electrolyte cannot exit into the measuring medium. The fluidelectrolyte can be a liquid electrolyte or a gel electrolyte.

During the operation of an amperometric measuring probe, the formationof an excess or negative pressure relative to the ambient pressure inthe measuring medium may occur. This may occur, for example, duringtemperature oscillations or by a material exchange between theelectrolyte and the measuring medium caused by osmosis. Pressureequalization between the probe interior and the measuring medium canthen take place in the measuring probe described above via the pressurerelief valve according to the prior art. It must be taken into account,however, that electrolyte from the probe interior passes into themeasuring medium, which is not beneficial in all amperometric measuringprobes. In the event of functional failure of the pressure relief valvethat results in the formation of a high excess pressure in the probeinterior, it can also lead to tearing or detachment of the sensitivesensor membrane.

An embodiment of the measuring probe according to the present disclosureprovides that the measuring probe further comprise at least onespecifically gas-filled or evacuated compensation volume, which iscoupled to the probe interior in such a manner that a change in theprevailing pressure in the probe interior causes a change in volume ofthe compensation volume. Preferably, no material exchange between thecompensation volume and the probe interior takes place here. If anexcess or a negative pressure forms in the probe interior, a change inthe compensation volume can then act to reduce the mechanical stresscaused on the sensitive sensor membrane by the excess or negativepressure prevailing in the probe interior.

The at least one compensation volume can be separated from the probeinterior by a flexible specifically, elastic wall. The compensationvolume can, for example, be formed by a gas-filled or evacuated chamberin the first or the second housing part that is separated from the probeinterior by the flexible specifically, elastic wall, such as a membranemade of an elastomer. In this embodiment, the flexible, in particularelastic wall, can advantageously have a higher elasticity than thesensor membrane.

The compensation volume can be separated from the probe interior by aflexible wall that is flexible because of its design, e.g., if the wallthickness selected is very thin, so that the wall can yield to excesspressure.

In an additional embodiment, the at least one compensation volume can beformed by a chamber formed within the probe housing, which is, inparticular, open to the area surrounding the probe or the probe housing.The chamber can be formed as a blind- or through-hole within the secondhousing part.

In an alternate embodiment, the at least one compensation volume can beformed in an elastic plastic foam arranged within the probe interior.The plastic foam can be formed from an elastomer as a plastic body thatencloses a plurality of compensation volumes in the form of gas-filledpores.

The first and the second housing parts can be designed to beinterconnected in a detachable manner. A detachable connection of thissort is, for example, a positive or non-positive connection, such as aplug, clamp, or screw connection. Such a connection can, for example, beformed using two coupling components, wherein one coupling component,which is connected to the first housing part, is connected to a secondcoupling component, which is connected to the second housing part. Inthe case of a screw connection, the first coupling component is formed,for example, by a section of a first housing part provided with athread, and the second coupling component is formed by a section of thesecond housing part provided with a thread that is complementary to thethread of the first housing part. The at least one overflow channel canbe formed, for example, using a groove that runs between a surface ofthe first coupling component and a surface of the second couplingcomponent that abuts the surface of the first coupling component if thefirst and the second coupling components are connected.

The first housing part may, for example, have a first thread and thesecond housing part can have a second thread complementary to the firstthread, wherein the first and the second housing parts are detachablyconnected to each other by a screw connection of the first thread to thesecond thread. Advantageously, the first and the second housing partsare formed in an essentially cylindrical in particular, cylindricallysymmetrical manner. In a connected state, the first and the secondhousing parts in this case are essentially cylindrically symmetricalwith respect to a common housing axis.

The seal can also be designed as a sealing ring arranged on the side ofthe screw connection opposite the probe interior space, the outercircumference of which abuts an inner circumferential surface of thesecond housing part and the inner circumference of which abuts an outercircumferential surface of the first housing part. In this manner, thesealing ring seals the first and the second housing parts radially,relative to each other. In an alternate embodiment, the sealing ring canalso be arranged as an axial seal between mutually facing end orshoulder faces of the first and the second housing parts.

The at least one overflow channel can be formed by a groove runningessentially parallel to a cylindrical axis of the first and or thesecond housing part. If the first and the second housing parts can beconnected via a screw connection, the at least one overflow channel canbe formed via at least one groove running essentially parallel to thethread axis through the thread teeth of the first and/or the secondthread. The sealing ring is advantageously arranged in the region of anend of the groove facing away from the probe interior, so that thesealing ring compressed between the first and the second housing partsseals the groove and with it, the overflow channel with respect to thearea surrounding the measuring probe, if the first and the secondhousing parts are connected to each other.

Alternatively, the overflow channel can be formed by a hole runningthrough the wall of the first and/or the second housing part.

The sensor membrane can form a porous diffusion barrier between ameasuring medium and the sensor interior space, through which at leastthe analyte can diffuse from the measuring medium into the probeinterior.

In the probe interior, at least two electrodes can be arranged that areconnected in an electrically conducting manner to a measuring circuitarranged outside of the probe interior in particular, in or on thesecond housing part and wherein the measuring circuit is formed for thepurpose of applying and/or regulating a specified voltage between theelectrodes, detecting a current that in this arrangement flows throughthe electrolyte contained in the probe interior, and further processingand/or emitting a signal dependent upon the detected current as ameasurement signal representing the measured variable.

The method according to the present disclosure for filling an innerspace of a probe, particularly in a manner free of gas bubbles with afluid electrolyte in order to measure a measured variable representing aconcentration of an analyte in a measuring medium includes the fillingof a fluid electrolyte into a first housing part that is designed in theshape of an, in particular, cylindrical cap that is closed off on afront end by a sensor membrane, and the manufacture of a connection thatcan be detached specifically, one designed as a screw or plug connectionbetween the first housing part and the second housing part wherein thefirst housing part and the second housing parts are moved towards eachother along a (notional) surface normal of the sensor membrane in such amanner that a partial section of the second housing part is guided intothe cap at a rear end opposite the sensor membrane, and a partial volumeof the electrolyte contained in the first housing part is displaced, sothat this partial volume flows out from the first housing part via anoverflow channel.

The sealing of the probe interior enclosed by the first housing part andthe second housing part via a seal located on a wall of the firsthousing part and a wall of the second housing part, in that the movementof the first and the second housing parts with respect to each other ismaintained so long as the seal between the wall of the first housingpart and the wall of the second housing part is compressed in a sealedmanner and simultaneously closes off the overflow channel.

The method can be carried out using the previously described measuringprobe according to the present disclosure in one of the describedembodiments.

The method can further comprise the preparation of at least one,specifically gas-filled or evacuated compensation volume, which iscoupled to the probe interior in such a manner that a change in theprevailing pressure in the probe interior causes a change in volume ofthe compensation volume in particular, without the occurrence of amaterial exchange between the compensation volume and the probeinterior.

The provision of the at least one compensation volume can comprise thecreation of one closed chamber in particular, in the second housing partvia a flexible specifically, elastic wall such that the flexiblespecifically, elastic wall is arranged in a section of the secondhousing part, which is in contact with the probe interior space when thedetachable connection is created between the first and the secondhousing parts.

The provision of the at least one compensation volume can comprise thearrangement of an elastic plastic foam in the probe chamber that has aplastic body, which encloses a plurality of compensation volumes in theform of gas-filled pores. The plastic body can, for example, be formedfrom an elastomer.

The first housing part can have first fastening means and the secondhousing part a second fastening means complementary to the firstfastening means, the first and the second fastening means serving toform a detachable, specifically positive or non-positive connection ofthe first housing part to the second housing part. The connection of thefirst to the second housing part can be accomplished, for example, bymeans of a clamp, plug, or screw connection.

Advantageously, the first housing part can have a first thread and thesecond housing part a second thread complementary to the first thread,wherein the creation of the detachable connection between the first andthe second housing parts comprises the formation of a screw connectionbetween the first and the second threads, and the seal is designed as asealing ring arranged on the side of the screw connection opposite theprobe interior space, the inner circumference of which abuts an outercircumferential surface of the second housing part and the outercircumference of which abuts an inner circumferential surface of thefirst housing part, and the at least one overflow channel is formed byat least one groove running essentially parallel to the thread axisthrough the thread teeth of the first and/or the second thread.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is explained in further detail below on the basisof the exemplary embodiments shown in the illustrations. The figuresshow:

FIG. 1 shows a schematic sectional illustration of an end section of anamperometric measuring probe provided for contact with a measuringmedium according to a first exemplary embodiment;

FIG. 2 shows a schematic illustration of a housing part of theamperometric measuring probe depicted in FIG. 1;

FIG. 3 shows a schematic sectional illustration of the measuring probedepicted in FIG. 1 in a state of excess pressure in the probe interior;

FIG. 4 shows a schematic sectional illustration of an end section of anamperometric probe provided for contact with a measuring mediumaccording to another exemplary embodiment; and

FIG. 5 shows a schematic sectional illustration of an end section of anamperometric measuring probe provided for contact with a measuringmedium according to a further exemplary embodiment.

DETAILED DESCRIPTION

In FIG. 1, a front section of an amperometric measuring probe 1 forimmersion in a measuring medium is shown in a longitudinalcross-section. The measuring probe 1 includes a probe housing 3, whichis formed from a first housing part 5 and a second housing part 7 thatare detachably interconnected via a screw connection. Probe housing 3 isessentially cylindrically symmetrical in the section illustrated, firsthousing part 5 and second housing part 7 having a common cylinder axisin their connected state. The housing parts can be made of a plastic,e.g., polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVDF), or of a metal. In the latter case,electrical insulation of the metallic housing is provided from theelectrodes described more fully herein.

First housing part 5 is designed in the form of a cap. On its frontside, i.e., the end opposite second housing part 7, it has a sensormembrane 9 that seals the first housing part 5 at this end. Projections11 surrounding sensor membrane 9 are provided on the front end of firsthousing part 5 for protection of sensor membrane 9 from mechanicaldamage. On its other end, first housing part 5 has an internal thread 13that serves to connect the first housing part 5 to the second housingpart 7.

The second housing part 7 includes an external thread 17 complementaryto internal thread 13 on an anterior, i.e., facing towards first housingpart 5, end section 15. In the illustration shown in FIG. 1, threads 13and 17 are detachably interconnected so that second housing part 7 sealsfirst housing part 5 at the back. The two connected housing part 5 and 7enclose a probe interior 23. Anterior end section 15 of second housingpart 7 has a circumferential, annular groove 19 in which a sealing ring21 is arranged. The groove 19 and sealing ring 21 are arranged on theside of the screw connection opposite the probe interior 23. The sealingring 21 can be formed from an elastomer, for example, from a commonsealing material known from the prior art, such as ethylene propylenediene monomer (EPDM), fluoroelastomers (FKM), or Nitrile butadienerubber (NBR). When first housing part 5 and second housing part 7 areconnected to each other, sealing ring 21 abuts the inner wall of firsthousing part 5 and the outer wall of second housing part 7 and, thus,seals probe interior 23, which is enclosed by the first and secondhousing parts 5, 7. Probe interior 23 is filled by a fluid electrolyte.

The second housing part 7 further includes a cylindrical probe shaft 25,of which only a front section is illustrated in FIG. 1. On its frontend, i.e., the end facing first housing part 5, probe shaft 25 has acylindrical electrode body 27 that extends into probe interior 23, thecross-section of which is reduced compared to the cross-section of probeshaft 25. Electrode body 27 is made of an electrically insulatingmaterial, for example, glass or plastic such as polyether ether ketone(PEEK) or PVC. Electrode body 27 encapsulates an electrically conductivemeasuring electrode 29 and electrically insulates the measuringelectrode 29, except for its end face 31 with respect to theelectrolytes contained in probe interior 23. End face 31 of measuringelectrode 29 and the end face of electrode body 27 surrounding themeasuring electrode 29 abut, at least partially, sensor membrane 9, sothat there is only a thin electrolyte film between end face 31 ofmeasuring electrode 29 and sensor membrane 9. The end face of electrodebody 27 can have a structure that includes raised regions anddepressions which are designed in such a manner that electrolyte canreach across the depressions in the region between end face 31 ofmeasuring electrode 29 and sensor membrane 9. Alternately oradditionally, a supporting grid can be provided between measuringelectrode 29 and sensor membrane 9.

Measuring electrode 29 can, for example, be made of a metal, inparticular a precious metal. Inside probe interior 23, an additionalelectrode is arranged that serves as a counter electrode (not shown inFIG. 1, for the sake of clarity) that can be designed as a ring sitting,for example, on electrode body 27. Optionally, a third electrode can bearranged in probe interior 23 that acts as a reference electrode forsetting a potential of measuring electrode 29. The electrodes areconnected in an electrically conductive manner to a measuring circuitarranged outside probe interior 23, for example, within probe shaft 25or in a housing part of the measuring probe connected to probe shaft 25.The measuring circuit is designed to apply or regulate a current betweenthe measuring electrode and the counter electrode to measure a currentflowing through the electrolyte and to create and emit a measurementsignal based upon the measured current strength. The measurement signalcan, for example, be output to a data processing device such as acomputer, a measuring transducer, or a controller connected to themeasuring circuit.

Front end section 15 of second housing part 7 surrounds a rear sectionof electrode body 27 so as to form a ring chamber 37 extending aroundelectrode body 27 and open to probe interior 23. Arranged in the ringchamber 37 is a hollow, cylindrical foam body 39, which is made from anelastomer and has a plurality of gas-filled pores. Foam body 39 can beformed from a silicone foam, for example. The foam body 39 acts as acompensation volume for equalizing pressure fluctuations inside theprobe interior, as explained in more detail herein.

In FIG. 2, second housing part 7 is represented in a separate schematicside view. Identical parts of housing part 7 are indicated by the samereference characters in FIG. 1 and FIG. 2. Thread teeth 33 of outerthread 17 arranged on front section 15 are broken by a groove 35extending parallel to the thread axis A of outer thread 17. The groove35 serves to form an overflow channel communicating with probe interior23.

In order to fill the probe interior with an essentially gas-bubble-freeelectrolyte, for example, during the manufacture of measuring probe 1 orin the course of maintenance measures in which first housing part 5 isexchanged for an identical housing part in order to replace sensormembrane 31 the procedure can be undertaken on measuring probe 1, whichis illustrated in FIG. 1 and FIG. 2, as follows. If the two housings 5,7 are separated from each other, the interior volume of cap-shapedhousing part 5 is larger than the volume of probe interior 23 enclosedby first and second housing parts 5, 7 in a connected state, because endsection 15 and electrode body 27 take up parts of the interior volume ofhousing part 5. Therefore, if first housing part 5 is fully, or almostfully, filled with electrolyte before the connection of second housingpart 7, upon connection of the housing parts, electrolyte from probeinterior 23 is forced through electrode body 27, and possibly alsothrough front end section 15 of second housing part 7 that is providedwith outer thread 17. During the screwing together of housing parts 5and 7, electrolyte can exit via the overflow channel formed by thegroove 35 that communicates with probe interior 23 and the areasurrounding housing 3. Only if second housing part 7 is screwed so farinto first housing part 5 that sealing ring 21 is compressed between theinterior wall of first housing part 5 and the outer wall of secondhousing part 7, and thus seals probe interior 23 as well as the overflowchannel (i.e., the groove 35), can electrolyte no longer leak out ofprobe interior 23.

This method ensures that probe interior 23 is free of gas bubbles thatcould disrupt a measurement using measuring probe 1.

If excess pressure or a pressure drop occurs in probe interior 23 duringthe screwing together of housing parts 5, 7 or during subsequentoperation, the foam body 39 can function as a compensation volume, inorder to reduce the pressure affecting sensor membrane 9 and theresulting mechanical damage to sensor membrane 9. Foam body 39 isdesigned in such a manner that it has a higher elasticity than sensormembrane 9. An increase in pressure in probe interior 23 then causesfoam body 39 or the gas-filled pores contained in foam body 39 todecrease their volume, and thereby reduce or compensate for the pressureincrease. Exemplary compression of foam body 39 is illustrated in FIG.3, which shows a schematic illustration of measuring probe 1 illustratedin FIG. 1, in which the volume of foam body 39 is only half as large asin the illustration in FIG. 1 because of a pressure increase in probeinterior 23.

As an additional exemplary embodiment of the present disclosure, FIG. 4shows a measuring probe 42 that is essentially identically designed tomeasuring probe 1 described in reference to FIGS. 1 through 3, whichhas, however, a compensation volume designed in the form of a gas-filledchamber, instead of a foam body. The parts of measuring probe 42 thatare designed to be identical to the corresponding parts of measuringprobe 1 according to FIGS. 1 through 3 are provided with the samereference characters. Like measuring probe 1, measuring probe 42 isequipped with a cap-shaped first housing part 5 that is designed to beidentical here to the corresponding first housing part of measuringprobe 1. A second housing part 43 is again detachably connected to firsthousing part 5 via a screw connection between an interior thread 13 offirst housing part 5 and an outer thread 17 of second housing part 43and, together with first housing part 5, encloses a probe interior 23. Afluid electrolyte is accommodated in probe interior 23. On its front endsection facing first housing part 5, second housing part 43 has acylindrical electrode body 27 that electrically insulates a measuringelectrode 29 up to its end face 31, in relation to the electrolyte.

As in measuring probe 1, measuring probe 42 includes an overflow channelrunning through the screw connection of both housing parts 5, 43 that isformed by a groove 35 running through the thread teeth of outer thread17 of second housing part 43. It is clear that other detachableconnection technologies are also suitable in place of a screw connectionfor connecting first housing part 5 to second housing part 43. In thiscase, the overflow channel can also be formed by a groove running in thefirst or the second housing part. Completely analogous to the exemplaryembodiments described in reference to FIGS. 1 through 3, probe interior23 of measuring probe 42 described in FIG. 4 can also be filled withgas-bubble-free electrolyte in the manner described, if first housingpart 5 is first filled with an electrolyte volume that is greater thanthe volume of probe interior 23 enclosed by first housing part 5 andsecond housing part 43 in a connected state, so that, during connectionof housing parts 5 and 43, electrolyte is forced through the overflowchannel out of the housing up until sealing ring 21 tightly seals theoverflow channel and probe interior 23.

A gas-filled chamber 45 in the form of a blind hole that is separatedfrom the probe interior 23 by a flexible, specifically elastic, wall 47is provided in second housing part 43 of measuring probe 42. Wall 47 canbe formed by an elastic membrane. In order to ensure that wall 47 has ahigher elasticity than membrane 9, it can be formed from a softerpolymer material specifically, an elastomer and/or have a smallerthickness than sensor membrane 9. Wall 47 can be formed as a plasticmembrane, such as from PTFE, PVDF, polysulfones (PES), or polyethyleneterephthalate (PET). In the event of a pressure change in probe interior23, the gas contained in chamber 45 can expand or be compressed, andthus serve to compensate for the pressure change. Mechanical stress tosensor membrane 9 caused by pressure changes in probe interior 23 andthe danger of damage to or detachment of sensor membrane 9 are thusminimized.

A measuring probe 54 is schematically represented in FIG. 5 as a furtherexemplary embodiment of the present disclosure. Measuring probe 54 isdesigned essentially identically to measuring probe 42 illustrated inFIG. 5. Identically designed parts of the measuring probes 54, 42, and 1shown in the figures are indicated using identical reference characters.

The only difference between measuring probe 42 shown in FIG. 4 andmeasuring probe 54 shown in FIG. 5 is in the design of the compensationvolume. In measuring probe 54, the compensation volume is formed by adegasification channel 55, which is closed on its end facing probeinterior 23 by an elastic wall 57, and is open to the area surroundingmeasuring probe 54 at its other end. Elastic wall 57 has a higherelasticity than sensor membrane 9, so that stress to sensor membrane 9is minimized by a pressure change in probe interior 23, as alreadydescribed above in reference to FIG. 4. It is either drawn here into theinterior of degasification channel 55 or bulges into probe interior 23.The gas volume consequently increases or decreases within degasificationchannel 55, and thus acts as a compensation volume.

The invention claimed is:
 1. A measuring probe for measuring a measuredvariable representing a concentration of an analyte in a measuringmedium, comprising: a probe housing including a first housing part and asecond housing part, the first housing part generally having a cap shapeclosed on a front end by a sensor membrane and having a detachableconnection to the second housing part on a rear end opposite the frontend such that the second housing part closes the first housing part atthe rear end, thereby defining a probe interior, wherein the sensormembrane seals the probe interior at the front end, and wherein thedetachable connection is a screw or plug connection; a flowable fluidelectroyte contained within the probe interior; an overflow channel incommunication with the probe interior; and a seal disposed between afirst wall of the first housing part and a second wall of the secondhousing part such that the seal abuts the probe interior and seals offthe probe interior from the exterior of the measurement probe andsimultaneously seals off the overflow channel opposite the probeinterior; wherein the first housing part and the second housing part arestructured so as to be connected to each other via a positive and/ornon-positive connection between a first coupling component connected tothe first housing part and a second coupling component connected to thesecond housing part, and wherein the overflow channel is defined by agroove extending between a first surface of the first coupling componentand a second surface of the second coupling component abutting the firstsurface when the first coupling component and the second couplingcomponent are connected.
 2. The measuring probe of claim 1, furthercomprising a gas-filled or evacuated compensation volume coupled to theprobe interior such that a change in a prevailing pressure in the probeinterior causes a change in a volume of the compensation volume whilepreventing a material exchange between the compensation volume and theprobe interior.
 3. The measuring probe of claim 2, wherein thecompensation volume is separated from the probe interior by a flexibleelastic wall.
 4. The measuring probe of claim 3, wherein the elasticwall has a higher elasticity than the sensor membrane.
 5. The measuringprobe of claim 2, wherein the compensation volume is a chamber that isopen to the exterior of the probe interior.
 6. The measuring probe ofclaim 5, wherein the chamber is a blind or through hole within thesecond housing part.
 7. The measuring probe of claim 2, wherein thecompensation volume is embodied in an elastic foam disposed within theprobe interior having a body that encloses a plurality of gas-filledpores, which define the compensation volume.
 8. The measuring probe ofclaim 1, wherein the first housing part has a first thread and thesecond housing part has a second thread complementary to the firstthread, and wherein the detachable connection of the first housing partand the second housing part is a screw connection between the firstthread to the second thread.
 9. The measuring probe of claim 8, whereinthe seal is embodied as a sealing ring disposed on a side of the screwconnection opposite the probe interior, the sealing ring having an outerperiphery that abuts an inner peripheral surface of the first housingpart and having an inner periphery that abuts an outer peripheralsurface of the second housing part.
 10. The measuring probe of claim 8,wherein the overflow channel is defined by at least one groove extendingparallel to a thread axis through thread teeth of the first threadand/or the second thread.
 11. The measuring probe of claim 1, whereinthe sensor membrane forms a porous diffusion barrier between a measuringmedium and the probe interior through which at least the analyte candiffuse from the measuring medium into the probe interior.
 12. Themeasuring probe of claim 1, wherein disposed in the probe interior areat least two electrodes electrically connected with a measuring circuitarranged outside of the probe interior in or on the second housing part,and wherein the measuring circuit is configured to apply and/or regulatea specified voltage between the at least two electrodes, to detect acurrent that thereby flows through the electrolyte contained within theprobe interior, and to process and/or emit a signal dependent upon thedetected current as a measurement signal representing the measuredvariable.
 13. A method for filling in a manner free of gas bubbles aprobe interior of a probe for measuring a measured variable representinga concentration of an analyte in a measuring medium using a fluidelectrolyte, comprising: filling a first housing part of a probe with afluid electrolyte, the first part having the shape of a cylindrical capclosed on a front end by a sensor membrane; assemblying a detachableconnection, structured as a screw or plug connection, between the firsthousing part and a second housing part of the probe, wherein the firsthousing part and second housing part are moved toward each other along asurface normal of the sensor membrane such that a partial section of thesecond housing part extends into the first housing part at a rear endopposite the sensor membrane, thereby defining a probe interior of theprobe for containing the electrolyte, and a partial volume of theelectrolyte contained in the first housing part is displaced and flowsout of the first housing part via an overflow channel; sealing the probeinterior using a seal disposed between a first wall of the first housingpart and a second wall of the second housing part, wherein during theassemblying, the first housing part and the second housing part aremoved toward each other until the seal between the first wall and thesecond wall is compressed in a sealed manner and simultaneously closesoff the overflow channel; and providing a gas-filled or evacuatedcompensation volume in the second housing part, the compensation volumecoupled to the probe interior such that a change in a prevailingpressure in the probe interior causes a change in a volume of thecompensation volume while preventing a material exchange between thecompensation volume and the probe interior.
 14. The method of claim 13,wherein providing the compensation volume includes creating in thesecond housing part a chamber closed off by a flexible, elastic wallthat is arranged in a section of the second housing part that is incontact with the probe interior when the detachable connection isassembled between the first housing part and the second housing part.15. The method of claim 13, wherein providing the compensation volumeincludes arranging in the probe interior an elastic plastic foam havinga body that encloses a plurality of gas-filled pores, which define thecompensation volume.
 16. The method of claim 13, wherein: the firsthousing part includes a first thread and the second housing partincludes a second thread complementary to the first thread; theassemblying of the detachable connection between the first housing partand the second housing part includes making a screw connection betweenthe first thread and the second thread; the seal is embodied as asealing ring disposed on a side of the screw connection opposite theprobe interior, the sealing ring having an inner circumference thatabuts an outer circumferential surface of the second housing part andhaving an outer circumference that abuts an inner circumferentialsurface of the first housing part; and the overflow channel is a groovethrough thread teeth of the first thread and/or the second thread, thegroove extending parallel to a thread axis of the first thread and/orthe second thread.